The present invention relates to a sampling scanning probe microscope, and more specifically, is directed to a sampling scanning probe microscope in which a cantilever is reciprocated along upper/lower directions on a surface of a sample, so that shape information and physical information about the sample surface can be obtained.
As a method for observing a shape and a physical characteristic of a sample surface by employment of the conventional scanning probe microscope, there are a contact mode and a tapping mode. The contact mode is well known in the field. For example, in this contact mode, as shown in FIG. 9, a probe 62 provided on a tip portion of a cantilever 61 is brought in contact with a surface of a sample 60 so as to scan the surface of the sample 60. At this time, deflection of the cantilever 61 is detected by detecting deviation of reflection of laser light 63 irradiated on one point of a rear portion of the cantilever 61 by using the four-split electrode 64. A feedback signal is produced by a circuit (not shown) from the sensing signal output by the four-split electrode 64. This feedback signal is applied to a piezoelectric electrode (not shown) for moving a sample base 65 in a fine mode along the upper/lower directions. As a result, such a control operation is carried out. That is, the sample surface is continuously traced by the probe 62. When this feedback signal is sampled plural times equal to the pixel number and then the sampled feedback signals are entered into the image display apparatus, the shape of the surface of the sample 60 can be imaged.
On the other hand, in the tapping mode, as represented in FIG. 10A, for example, a piezoelectric plate 70 is fixed on an end of the cantilever 61, which is located opposite to the probe 62. As indicated in FIG. 10B, an electric signal having a resonant frequency (e.g., 100 KHz) of the cantilever 61 is supplied by an oscillator 71 to the piezoelectric plate 70. Then, the probe 62 of this cantilever 61 continuously taps the surface of the sample 60. The feedback control is carried out by using the piezoelectric element of the sample base 65 in such a manner that an attenuation amount of this amplitude becomes constant. The feedback signal is sampled plural times equal to the pixel number and then the sampled feedback signals are supplied to an image display apparatus, so that the shape of the sample surface is displayed on this image display apparatus.
FIG. 11 schematically illustrates an enlarged diagram of the sample width "s" of FIG. 10A, and the tapping positions of the probe 62. In this drawing, symbol "a" shows a contour of a sample surface, and the respective points "b" represent a trail of a trace of the probe in the probe tapping mode. A time period of this tapping is set to, for example, 1/10.sup.5 seconds.
However, the above-described conventional techniques have the following problems. That is, in the contact mode, since the probe 62 is continuously in contact with the sample 60, the depression force having the magnitude of on the order of, for example, 10 to 100 nN (nanonewton) is continuously exerted on the surface of the sample 60. At the same time, since the probe 62 is scanned, a force along the transverse direction of the scanning direction is applied. As a consequence, there are problems in that the surface of the sample 60 is readily damaged, and the needle tip of the probe 62 is easily abraded, resulting in a short lifetime thereof.
On the other hand, in the tapping mode, since the surface of the sample 60 is continuously tapped by the probe in the resonant frequency of the cantilever 61, for example, when this resonant frequency is selected to be 100 KHz, the sample surface is continuously tapped by the probe 10.sup.5 times per second. As a result, there is another problem in that the surface of the sample 60 is readily damaged.
Also, there is the below-mentioned common problem in the contact mode and the tapping mode. That is, normally speaking, approximately 512 pixels, or 1,000 pixels per 1 second are employed as the number of pixels used in the above-described image display apparatus. However, as to the surface information of the sample 60 acquired in both the contact mode and the tapping mode, a substantially infinite number of pixels is employed in the contact mode, and approximately 10.sup.5 pixels are employed in the tapping mode, which is considerably larger than the above-described pixel number of pixels. In other words, a large number of useless pixel information is discarded. Even when such discarded pixel information is acquired, there is a problem in that since the probe 62 continuously depresses, or taps the surface of the sample 60, the sample 60 is damaged. Also, the trace speed of the probe on the sample surface depends upon the scanned width of the sample. Therefore, there is a further problem in that the wider the scanned width of this sample is widened, the slower the scanning speed is decreased.
An object of the present invention is to solve the above-described problems of the prior art, and is to provide a sampling scanning probe microscope capable of reducing a damage to a sample, and further capable of extending the lifetime of a probe. Another object of the present invention is to provide a sampling scanning probe microscope capable of making a scanning speed constant irrespective of a scanned width of a sample.